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674 lines
24 KiB
Python
674 lines
24 KiB
Python
# mssql/pyodbc.py
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# Copyright (C) 2005-2022 the SQLAlchemy authors and contributors
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# <see AUTHORS file>
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#
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# This module is part of SQLAlchemy and is released under
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# the MIT License: https://www.opensource.org/licenses/mit-license.php
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r"""
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.. dialect:: mssql+pyodbc
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:name: PyODBC
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:dbapi: pyodbc
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:connectstring: mssql+pyodbc://<username>:<password>@<dsnname>
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:url: https://pypi.org/project/pyodbc/
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Connecting to PyODBC
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--------------------
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The URL here is to be translated to PyODBC connection strings, as
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detailed in `ConnectionStrings <https://code.google.com/p/pyodbc/wiki/ConnectionStrings>`_.
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DSN Connections
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^^^^^^^^^^^^^^^
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A DSN connection in ODBC means that a pre-existing ODBC datasource is
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configured on the client machine. The application then specifies the name
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of this datasource, which encompasses details such as the specific ODBC driver
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in use as well as the network address of the database. Assuming a datasource
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is configured on the client, a basic DSN-based connection looks like::
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engine = create_engine("mssql+pyodbc://scott:tiger@some_dsn")
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Which above, will pass the following connection string to PyODBC::
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DSN=some_dsn;UID=scott;PWD=tiger
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If the username and password are omitted, the DSN form will also add
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the ``Trusted_Connection=yes`` directive to the ODBC string.
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Hostname Connections
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^^^^^^^^^^^^^^^^^^^^
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Hostname-based connections are also supported by pyodbc. These are often
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easier to use than a DSN and have the additional advantage that the specific
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database name to connect towards may be specified locally in the URL, rather
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than it being fixed as part of a datasource configuration.
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When using a hostname connection, the driver name must also be specified in the
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query parameters of the URL. As these names usually have spaces in them, the
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name must be URL encoded which means using plus signs for spaces::
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engine = create_engine("mssql+pyodbc://scott:tiger@myhost:port/databasename?driver=ODBC+Driver+17+for+SQL+Server")
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Other keywords interpreted by the Pyodbc dialect to be passed to
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``pyodbc.connect()`` in both the DSN and hostname cases include:
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``odbc_autotranslate``, ``ansi``, ``unicode_results``, ``autocommit``,
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``authentication``.
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Note that in order for the dialect to recognize these keywords
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(including the ``driver`` keyword above) they must be all lowercase.
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Multiple additional keyword arguments must be separated by an
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ampersand (``&``), not a semicolon::
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engine = create_engine(
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"mssql+pyodbc://scott:tiger@myhost:49242/databasename"
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"?driver=ODBC+Driver+17+for+SQL+Server"
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"&authentication=ActiveDirectoryIntegrated"
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)
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The equivalent URL can be constructed using :class:`_sa.engine.URL`::
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from sqlalchemy.engine import URL
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connection_url = URL.create(
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"mssql+pyodbc",
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username="scott",
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password="tiger",
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host="myhost",
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port=49242,
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database="databasename",
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query={
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"driver": "ODBC Driver 17 for SQL Server",
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"authentication": "ActiveDirectoryIntegrated",
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},
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)
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Pass through exact Pyodbc string
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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A PyODBC connection string can also be sent in pyodbc's format directly, as
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specified in `the PyODBC documentation
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<https://github.com/mkleehammer/pyodbc/wiki/Connecting-to-databases>`_,
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using the parameter ``odbc_connect``. A :class:`_sa.engine.URL` object
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can help make this easier::
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from sqlalchemy.engine import URL
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connection_string = "DRIVER={SQL Server Native Client 10.0};SERVER=dagger;DATABASE=test;UID=user;PWD=password"
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connection_url = URL.create("mssql+pyodbc", query={"odbc_connect": connection_string})
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engine = create_engine(connection_url)
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.. _mssql_pyodbc_access_tokens:
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Connecting to databases with access tokens
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Some database servers are set up to only accept access tokens for login. For
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example, SQL Server allows the use of Azure Active Directory tokens to connect
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to databases. This requires creating a credential object using the
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``azure-identity`` library. More information about the authentication step can be
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found in `Microsoft's documentation
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<https://docs.microsoft.com/en-us/azure/developer/python/azure-sdk-authenticate?tabs=bash>`_.
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After getting an engine, the credentials need to be sent to ``pyodbc.connect``
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each time a connection is requested. One way to do this is to set up an event
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listener on the engine that adds the credential token to the dialect's connect
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call. This is discussed more generally in :ref:`engines_dynamic_tokens`. For
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SQL Server in particular, this is passed as an ODBC connection attribute with
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a data structure `described by Microsoft
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<https://docs.microsoft.com/en-us/sql/connect/odbc/using-azure-active-directory#authenticating-with-an-access-token>`_.
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The following code snippet will create an engine that connects to an Azure SQL
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database using Azure credentials::
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import struct
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from sqlalchemy import create_engine, event
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from sqlalchemy.engine.url import URL
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from azure import identity
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SQL_COPT_SS_ACCESS_TOKEN = 1256 # Connection option for access tokens, as defined in msodbcsql.h
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TOKEN_URL = "https://database.windows.net/" # The token URL for any Azure SQL database
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connection_string = "mssql+pyodbc://@my-server.database.windows.net/myDb?driver=ODBC+Driver+17+for+SQL+Server"
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engine = create_engine(connection_string)
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azure_credentials = identity.DefaultAzureCredential()
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@event.listens_for(engine, "do_connect")
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def provide_token(dialect, conn_rec, cargs, cparams):
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# remove the "Trusted_Connection" parameter that SQLAlchemy adds
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cargs[0] = cargs[0].replace(";Trusted_Connection=Yes", "")
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# create token credential
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raw_token = azure_credentials.get_token(TOKEN_URL).token.encode("utf-16-le")
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token_struct = struct.pack(f"<I{len(raw_token)}s", len(raw_token), raw_token)
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# apply it to keyword arguments
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cparams["attrs_before"] = {SQL_COPT_SS_ACCESS_TOKEN: token_struct}
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.. tip::
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The ``Trusted_Connection`` token is currently added by the SQLAlchemy
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pyodbc dialect when no username or password is present. This needs
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to be removed per Microsoft's
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`documentation for Azure access tokens
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<https://docs.microsoft.com/en-us/sql/connect/odbc/using-azure-active-directory#authenticating-with-an-access-token>`_,
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stating that a connection string when using an access token must not contain
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``UID``, ``PWD``, ``Authentication`` or ``Trusted_Connection`` parameters.
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.. _azure_synapse_ignore_no_transaction_on_rollback:
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Avoiding transaction-related exceptions on Azure Synapse Analytics
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Azure Synapse Analytics has a significant difference in its transaction
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handling compared to plain SQL Server; in some cases an error within a Synapse
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transaction can cause it to be arbitrarily terminated on the server side, which
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then causes the DBAPI ``.rollback()`` method (as well as ``.commit()``) to
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fail. The issue prevents the usual DBAPI contract of allowing ``.rollback()``
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to pass silently if no transaction is present as the driver does not expect
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this condition. The symptom of this failure is an exception with a message
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resembling 'No corresponding transaction found. (111214)' when attempting to
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emit a ``.rollback()`` after an operation had a failure of some kind.
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This specific case can be handled by passing ``ignore_no_transaction_on_rollback=True`` to
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the SQL Server dialect via the :func:`_sa.create_engine` function as follows::
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engine = create_engine(connection_url, ignore_no_transaction_on_rollback=True)
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Using the above parameter, the dialect will catch ``ProgrammingError``
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exceptions raised during ``connection.rollback()`` and emit a warning
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if the error message contains code ``111214``, however will not raise
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an exception.
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.. versionadded:: 1.4.40 Added the
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``ignore_no_transaction_on_rollback=True`` parameter.
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Enable autocommit for Azure SQL Data Warehouse (DW) connections
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Azure SQL Data Warehouse does not support transactions,
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and that can cause problems with SQLAlchemy's "autobegin" (and implicit
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commit/rollback) behavior. We can avoid these problems by enabling autocommit
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at both the pyodbc and engine levels::
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connection_url = sa.engine.URL.create(
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"mssql+pyodbc",
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username="scott",
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password="tiger",
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host="dw.azure.example.com",
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database="mydb",
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query={
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"driver": "ODBC Driver 17 for SQL Server",
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"autocommit": "True",
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},
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)
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engine = create_engine(connection_url).execution_options(
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isolation_level="AUTOCOMMIT"
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)
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Avoiding sending large string parameters as TEXT/NTEXT
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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By default, for historical reasons, Microsoft's ODBC drivers for SQL Server
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send long string parameters (greater than 4000 SBCS characters or 2000 Unicode
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characters) as TEXT/NTEXT values. TEXT and NTEXT have been deprecated for many
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years and are starting to cause compatibility issues with newer versions of
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SQL_Server/Azure. For example, see `this
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issue <https://github.com/mkleehammer/pyodbc/issues/835>`_.
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Starting with ODBC Driver 18 for SQL Server we can override the legacy
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behavior and pass long strings as varchar(max)/nvarchar(max) using the
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``LongAsMax=Yes`` connection string parameter::
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connection_url = sa.engine.URL.create(
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"mssql+pyodbc",
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username="scott",
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password="tiger",
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host="mssqlserver.example.com",
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database="mydb",
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query={
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"driver": "ODBC Driver 18 for SQL Server",
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"LongAsMax": "Yes",
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},
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)
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Pyodbc Pooling / connection close behavior
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------------------------------------------
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PyODBC uses internal `pooling
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<https://github.com/mkleehammer/pyodbc/wiki/The-pyodbc-Module#pooling>`_ by
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default, which means connections will be longer lived than they are within
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SQLAlchemy itself. As SQLAlchemy has its own pooling behavior, it is often
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preferable to disable this behavior. This behavior can only be disabled
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globally at the PyODBC module level, **before** any connections are made::
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import pyodbc
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pyodbc.pooling = False
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# don't use the engine before pooling is set to False
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engine = create_engine("mssql+pyodbc://user:pass@dsn")
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If this variable is left at its default value of ``True``, **the application
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will continue to maintain active database connections**, even when the
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SQLAlchemy engine itself fully discards a connection or if the engine is
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disposed.
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.. seealso::
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`pooling <https://github.com/mkleehammer/pyodbc/wiki/The-pyodbc-Module#pooling>`_ -
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in the PyODBC documentation.
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Driver / Unicode Support
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-------------------------
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PyODBC works best with Microsoft ODBC drivers, particularly in the area
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of Unicode support on both Python 2 and Python 3.
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Using the FreeTDS ODBC drivers on Linux or OSX with PyODBC is **not**
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recommended; there have been historically many Unicode-related issues
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in this area, including before Microsoft offered ODBC drivers for Linux
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and OSX. Now that Microsoft offers drivers for all platforms, for
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PyODBC support these are recommended. FreeTDS remains relevant for
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non-ODBC drivers such as pymssql where it works very well.
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Rowcount Support
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----------------
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Pyodbc only has partial support for rowcount. See the notes at
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:ref:`mssql_rowcount_versioning` for important notes when using ORM
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versioning.
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.. _mssql_pyodbc_fastexecutemany:
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Fast Executemany Mode
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---------------------
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The Pyodbc driver has added support for a "fast executemany" mode of execution
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which greatly reduces round trips for a DBAPI ``executemany()`` call when using
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Microsoft ODBC drivers, for **limited size batches that fit in memory**. The
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feature is enabled by setting the flag ``.fast_executemany`` on the DBAPI
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cursor when an executemany call is to be used. The SQLAlchemy pyodbc SQL
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Server dialect supports setting this flag automatically when the
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``.fast_executemany`` flag is passed to
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:func:`_sa.create_engine` ; note that the ODBC driver must be the Microsoft
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driver in order to use this flag::
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engine = create_engine(
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"mssql+pyodbc://scott:tiger@mssql2017:1433/test?driver=ODBC+Driver+13+for+SQL+Server",
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fast_executemany=True)
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.. warning:: The pyodbc fast_executemany mode **buffers all rows in memory** and is
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not compatible with very large batches of data. A future version of SQLAlchemy
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may support this flag as a per-execution option instead.
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.. versionadded:: 1.3
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.. seealso::
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`fast executemany <https://github.com/mkleehammer/pyodbc/wiki/Features-beyond-the-DB-API#fast_executemany>`_
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- on github
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.. _mssql_pyodbc_setinputsizes:
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Setinputsizes Support
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-----------------------
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The pyodbc ``cursor.setinputsizes()`` method can be used if necessary. To
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enable this hook, pass ``use_setinputsizes=True`` to :func:`_sa.create_engine`::
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engine = create_engine("mssql+pyodbc://...", use_setinputsizes=True)
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The behavior of the hook can then be customized, as may be necessary
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particularly if fast_executemany is in use, via the
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:meth:`.DialectEvents.do_setinputsizes` hook. See that method for usage
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examples.
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.. versionchanged:: 1.4.1 The pyodbc dialects will not use setinputsizes
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unless ``use_setinputsizes=True`` is passed.
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""" # noqa
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import datetime
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import decimal
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import re
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import struct
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from .base import BINARY
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from .base import DATETIMEOFFSET
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from .base import MSDialect
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from .base import MSExecutionContext
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from .base import VARBINARY
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from ... import exc
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from ... import types as sqltypes
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from ... import util
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from ...connectors.pyodbc import PyODBCConnector
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class _ms_numeric_pyodbc(object):
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"""Turns Decimals with adjusted() < 0 or > 7 into strings.
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The routines here are needed for older pyodbc versions
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as well as current mxODBC versions.
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"""
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def bind_processor(self, dialect):
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super_process = super(_ms_numeric_pyodbc, self).bind_processor(dialect)
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if not dialect._need_decimal_fix:
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return super_process
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def process(value):
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if self.asdecimal and isinstance(value, decimal.Decimal):
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adjusted = value.adjusted()
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if adjusted < 0:
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return self._small_dec_to_string(value)
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elif adjusted > 7:
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return self._large_dec_to_string(value)
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if super_process:
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return super_process(value)
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else:
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return value
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return process
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# these routines needed for older versions of pyodbc.
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# as of 2.1.8 this logic is integrated.
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def _small_dec_to_string(self, value):
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return "%s0.%s%s" % (
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(value < 0 and "-" or ""),
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"0" * (abs(value.adjusted()) - 1),
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"".join([str(nint) for nint in value.as_tuple()[1]]),
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)
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def _large_dec_to_string(self, value):
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_int = value.as_tuple()[1]
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if "E" in str(value):
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result = "%s%s%s" % (
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(value < 0 and "-" or ""),
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"".join([str(s) for s in _int]),
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"0" * (value.adjusted() - (len(_int) - 1)),
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)
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else:
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if (len(_int) - 1) > value.adjusted():
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result = "%s%s.%s" % (
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(value < 0 and "-" or ""),
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"".join([str(s) for s in _int][0 : value.adjusted() + 1]),
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"".join([str(s) for s in _int][value.adjusted() + 1 :]),
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)
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else:
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result = "%s%s" % (
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(value < 0 and "-" or ""),
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"".join([str(s) for s in _int][0 : value.adjusted() + 1]),
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)
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return result
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class _MSNumeric_pyodbc(_ms_numeric_pyodbc, sqltypes.Numeric):
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pass
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class _MSFloat_pyodbc(_ms_numeric_pyodbc, sqltypes.Float):
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pass
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class _ms_binary_pyodbc(object):
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"""Wraps binary values in dialect-specific Binary wrapper.
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If the value is null, return a pyodbc-specific BinaryNull
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object to prevent pyODBC [and FreeTDS] from defaulting binary
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NULL types to SQLWCHAR and causing implicit conversion errors.
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"""
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def bind_processor(self, dialect):
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if dialect.dbapi is None:
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return None
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DBAPIBinary = dialect.dbapi.Binary
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def process(value):
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if value is not None:
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return DBAPIBinary(value)
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else:
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# pyodbc-specific
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return dialect.dbapi.BinaryNull
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return process
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class _ODBCDateTimeBindProcessor(object):
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"""Add bind processors to handle datetimeoffset behaviors"""
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has_tz = False
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def bind_processor(self, dialect):
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def process(value):
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if value is None:
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return None
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elif isinstance(value, util.string_types):
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# if a string was passed directly, allow it through
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return value
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elif not value.tzinfo or (not self.timezone and not self.has_tz):
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# for DateTime(timezone=False)
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return value
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else:
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# for DATETIMEOFFSET or DateTime(timezone=True)
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#
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# Convert to string format required by T-SQL
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dto_string = value.strftime("%Y-%m-%d %H:%M:%S.%f %z")
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# offset needs a colon, e.g., -0700 -> -07:00
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# "UTC offset in the form (+-)HHMM[SS[.ffffff]]"
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# backend currently rejects seconds / fractional seconds
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dto_string = re.sub(
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r"([\+\-]\d{2})([\d\.]+)$", r"\1:\2", dto_string
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)
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return dto_string
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return process
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class _ODBCDateTime(_ODBCDateTimeBindProcessor, sqltypes.DateTime):
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pass
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class _ODBCDATETIMEOFFSET(_ODBCDateTimeBindProcessor, DATETIMEOFFSET):
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has_tz = True
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class _VARBINARY_pyodbc(_ms_binary_pyodbc, VARBINARY):
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pass
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class _BINARY_pyodbc(_ms_binary_pyodbc, BINARY):
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pass
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class MSExecutionContext_pyodbc(MSExecutionContext):
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_embedded_scope_identity = False
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|
|
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def pre_exec(self):
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|
"""where appropriate, issue "select scope_identity()" in the same
|
|
statement.
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|
|
|
Background on why "scope_identity()" is preferable to "@@identity":
|
|
https://msdn.microsoft.com/en-us/library/ms190315.aspx
|
|
|
|
Background on why we attempt to embed "scope_identity()" into the same
|
|
statement as the INSERT:
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|
https://code.google.com/p/pyodbc/wiki/FAQs#How_do_I_retrieve_autogenerated/identity_values?
|
|
|
|
"""
|
|
|
|
super(MSExecutionContext_pyodbc, self).pre_exec()
|
|
|
|
# don't embed the scope_identity select into an
|
|
# "INSERT .. DEFAULT VALUES"
|
|
if (
|
|
self._select_lastrowid
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|
and self.dialect.use_scope_identity
|
|
and len(self.parameters[0])
|
|
):
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self._embedded_scope_identity = True
|
|
|
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self.statement += "; select scope_identity()"
|
|
|
|
def post_exec(self):
|
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if self._embedded_scope_identity:
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# Fetch the last inserted id from the manipulated statement
|
|
# We may have to skip over a number of result sets with
|
|
# no data (due to triggers, etc.)
|
|
while True:
|
|
try:
|
|
# fetchall() ensures the cursor is consumed
|
|
# without closing it (FreeTDS particularly)
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|
row = self.cursor.fetchall()[0]
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|
break
|
|
except self.dialect.dbapi.Error:
|
|
# no way around this - nextset() consumes the previous set
|
|
# so we need to just keep flipping
|
|
self.cursor.nextset()
|
|
|
|
self._lastrowid = int(row[0])
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else:
|
|
super(MSExecutionContext_pyodbc, self).post_exec()
|
|
|
|
|
|
class MSDialect_pyodbc(PyODBCConnector, MSDialect):
|
|
supports_statement_cache = True
|
|
|
|
# mssql still has problems with this on Linux
|
|
supports_sane_rowcount_returning = False
|
|
|
|
execution_ctx_cls = MSExecutionContext_pyodbc
|
|
|
|
colspecs = util.update_copy(
|
|
MSDialect.colspecs,
|
|
{
|
|
sqltypes.Numeric: _MSNumeric_pyodbc,
|
|
sqltypes.Float: _MSFloat_pyodbc,
|
|
BINARY: _BINARY_pyodbc,
|
|
# support DateTime(timezone=True)
|
|
sqltypes.DateTime: _ODBCDateTime,
|
|
DATETIMEOFFSET: _ODBCDATETIMEOFFSET,
|
|
# SQL Server dialect has a VARBINARY that is just to support
|
|
# "deprecate_large_types" w/ VARBINARY(max), but also we must
|
|
# handle the usual SQL standard VARBINARY
|
|
VARBINARY: _VARBINARY_pyodbc,
|
|
sqltypes.VARBINARY: _VARBINARY_pyodbc,
|
|
sqltypes.LargeBinary: _VARBINARY_pyodbc,
|
|
},
|
|
)
|
|
|
|
def __init__(
|
|
self, description_encoding=None, fast_executemany=False, **params
|
|
):
|
|
if "description_encoding" in params:
|
|
self.description_encoding = params.pop("description_encoding")
|
|
super(MSDialect_pyodbc, self).__init__(**params)
|
|
self.use_scope_identity = (
|
|
self.use_scope_identity
|
|
and self.dbapi
|
|
and hasattr(self.dbapi.Cursor, "nextset")
|
|
)
|
|
self._need_decimal_fix = self.dbapi and self._dbapi_version() < (
|
|
2,
|
|
1,
|
|
8,
|
|
)
|
|
self.fast_executemany = fast_executemany
|
|
|
|
def _get_server_version_info(self, connection):
|
|
try:
|
|
# "Version of the instance of SQL Server, in the form
|
|
# of 'major.minor.build.revision'"
|
|
raw = connection.exec_driver_sql(
|
|
"SELECT CAST(SERVERPROPERTY('ProductVersion') AS VARCHAR)"
|
|
).scalar()
|
|
except exc.DBAPIError:
|
|
# SQL Server docs indicate this function isn't present prior to
|
|
# 2008. Before we had the VARCHAR cast above, pyodbc would also
|
|
# fail on this query.
|
|
return super(MSDialect_pyodbc, self)._get_server_version_info(
|
|
connection, allow_chars=False
|
|
)
|
|
else:
|
|
version = []
|
|
r = re.compile(r"[.\-]")
|
|
for n in r.split(raw):
|
|
try:
|
|
version.append(int(n))
|
|
except ValueError:
|
|
pass
|
|
return tuple(version)
|
|
|
|
def on_connect(self):
|
|
super_ = super(MSDialect_pyodbc, self).on_connect()
|
|
|
|
def on_connect(conn):
|
|
if super_ is not None:
|
|
super_(conn)
|
|
|
|
self._setup_timestampoffset_type(conn)
|
|
|
|
return on_connect
|
|
|
|
def _setup_timestampoffset_type(self, connection):
|
|
# output converter function for datetimeoffset
|
|
def _handle_datetimeoffset(dto_value):
|
|
tup = struct.unpack("<6hI2h", dto_value)
|
|
return datetime.datetime(
|
|
tup[0],
|
|
tup[1],
|
|
tup[2],
|
|
tup[3],
|
|
tup[4],
|
|
tup[5],
|
|
tup[6] // 1000,
|
|
util.timezone(
|
|
datetime.timedelta(hours=tup[7], minutes=tup[8])
|
|
),
|
|
)
|
|
|
|
odbc_SQL_SS_TIMESTAMPOFFSET = -155 # as defined in SQLNCLI.h
|
|
connection.add_output_converter(
|
|
odbc_SQL_SS_TIMESTAMPOFFSET, _handle_datetimeoffset
|
|
)
|
|
|
|
def do_executemany(self, cursor, statement, parameters, context=None):
|
|
if self.fast_executemany:
|
|
cursor.fast_executemany = True
|
|
super(MSDialect_pyodbc, self).do_executemany(
|
|
cursor, statement, parameters, context=context
|
|
)
|
|
|
|
def is_disconnect(self, e, connection, cursor):
|
|
if isinstance(e, self.dbapi.Error):
|
|
code = e.args[0]
|
|
if code in {
|
|
"08S01",
|
|
"01000",
|
|
"01002",
|
|
"08003",
|
|
"08007",
|
|
"08S02",
|
|
"08001",
|
|
"HYT00",
|
|
"HY010",
|
|
"10054",
|
|
}:
|
|
return True
|
|
return super(MSDialect_pyodbc, self).is_disconnect(
|
|
e, connection, cursor
|
|
)
|
|
|
|
|
|
dialect = MSDialect_pyodbc
|